[Vwdiesel] starting problem testing injectors

James Hansen jhsg at sasktel.net
Sat Mar 11 01:33:35 EST 2006

I don't have a lot of experience with diesels yet but what I have learned so
far with the VW's is that IMO injector troubles are more prone to cause bad
knocking, hammering noises in the engine when running, and roughness making
power.  If you have a normal sounding engine once warmed up the problem
probably isn't injectors.

Sorry, false.

Injectors can fail in a couple ways.  the pintle can stick open, or fail to
close fully, leading to the nailing, hammering noise that you refer to.
that's one way.

Other is to wear out.  The tiny hole in the schnozzle gets eroded from
passing a few thousand gallons of fuel through a hole the size of a frog's
nose hair , and it does not properly atomize the fuel after time.  This will
translate into poor starts, a loss in mileage, poor starts, symptoms of
timing being off, lack of response to timing changes, and poor starting.
The larger droplets of fuel just don't light up as well as smaller ones.

I've seen a set of injectors that were not leaking, but when tested,
practically spit it out in chunks.  Thing is, they were all the same, so the
idle was consistent, it didn't sound bad at all... just ran poorly, like the
timing was retarded... which it was effectively retarded when you allow for
the extra time for the larger drops of fuel to light off.
Your idle only goes to crap when some are good, and some are bad, or valve
adjustments are off.

It's pretty simple to diagnose.  compression and fuel at the right time.  A
gasser has ignition to go wrong, but with CI engines, there are really only
two things that are needed.
Usually, start with a timing and a valve adjustment if an early motor, then
check injector spray pattern (take them to a shop that has a BOSCH sign on
the door), if that's still all good and it runs like shit, then compression
test, to look for trouble with rings.  Beyond that... cranking speed.

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